(1) Field of the Invention
The present invention relates to the use of a food grade bacteria which produces 3-methyl-butanal for the preparation of a fermented meat product. This invention particularly relates to the process for developing an improved flavor and aroma in fermented meat particularly in dry or semi-dry sausages using a bacterial composition of a culture which produces 3-methyl-butanal. The present invention relates in one specific embodiment, to a method and compositions for producing fermented meats using a lactic acid producing culture in combination with a culture which produces 3-methyl-butanal and optionally with a culture(s) which produces red color. Alternatively, the culture which produces 3-methyl-butanal can be used to develop flavor in the meat and relying on the culture to produce lactic acid.
(2) Description of Related Art
Processes for dry and semi-dry sausage preparation are examples of conventional fermentations where acidity is generated to provide tang. Dry and semi-dry sausages vary in taste according to the meat source, i.e., pork, beef, veal, etc. and their different mixtures, the sugar, spices, and starter cultures used in processing. The fairly distinct categories of semi-dry sausage are known as summer sausage, cervelat, Thuringer, pork roll and lebanon bologna. Some dry sausages are Chorizos, hard salami, Genoa salami, German katenwurst, and Mettwurst salamis and various kind of Italian sausage such as Pepperoni and Cappicola. There are other dry and semi-dry sausages which can be produced by the present invention.
Dry and semi-dry sausages are generally distinguished from other types of sausages by the prior art in that they are fermented. The comminuted meat mixture is preferably mixed with added salt, spices, edible nitrite and/or nitrate for curing bacteria and sometimes acid forming chemicals. It is then stuffed into casing and fermented with the bacteria. Curing allows the edible nitrites, and nitrates upon subsequent reduction to nitrite, to form nitric oxide which in the presence of acids combines with the pigment in the meat to produce the red color usually associated with the sausage. It is the edible nitrites which generate the red color in the meat and more importantly which provide protection against the formation of botulism toxin by Clostridium botulinum growth (Varnam, A. H., and J. P. Sutherland Meat and meat products: technology, chemistry and microbiology, Chapter 7:317-353 (1995)). The meat can also be uncured.
The fermented sausage may be given a light or heavy smoke. The semi-dry sausages are sometimes cooked after the fermentation without an extensive drying period. The dry sausage is dried for various time periods under controlled humidity and temperature conditions, depending upon the nature of the end product. Because of this processing, the resulting sausages differ from other types of sausage, such as fresh, smoked, cured, cooked and the so-called new condition sausages.
A commonly used starter bacterium for fermenting meat to produce semi-dry or dry sausage is Pediococcus acidilactici because it rapidly produces large amounts of primarily lactic acid to lower the pH, which gives the final sausage its characteristic tang. This bacterium is commercially obtainable both in a frozen state as a concentrate and in a lyophilized state. It may be for instance the bacterium described in U.S. Pat. Nos. 3,561,977 and 3,960,664 to Olsen et al. U.S. Pat. No. 4,303,679 to Raccach describes the use of Pediococcus pentosaceus and metal salts for fermenting meats. U.S. Pat. No. 3,814,817 to Everson et al describes the use of Lactobacillus plantarum for fermenting meat.
Species of Micrococcus are also used in making sausage, particularly in Germany. W. German Patent No. 1,692,174 describes an unidentified strain of Micrococcus mixed with lactic acid forming bacteria, with substantial amounts of gluconic acid delta lactone (GDL) to rapidly lower the pH, and with polyphosphates, ascorbic acid and its sodium salts as pH regulators. GDL has a chemical acid taste and is undesirable for this reason.
The Micrococcus produce the red sausage color during the fermentation as discussed above. Microbiology Vol 26, No. 4 pp. 489 to 496 (1973) and U.S. Pat. No. 1,380,068 describe the importance of the naturally occurring micrococci in the meat on color development. U.S. Pat. No. 4,013,797 to Gryczka also describes the importance of using a high acid producing nitrate reducing bacteria characterized as Micrococcus sp. NRRL-B-8048. U.S. Pat. No. 4,147,807 to Gryczka et al describes the use of Micrococcus varians to develop the red color in meat.
U.S. Pat. No. 3,193,391 describes the use of various flavor producing bacteria from the families Lactobacillaceae and Micrococcaceae for preparing cured meats. This is a related fermentation process for flavor development on large sized meat sections.
Starter cultures play several important roles in the fermentation and ripening of dry and semi-dry sausages. The primary function of the starter culture is the acidification process by means of converting the sugar(s) added to the meat mixture into acid. Usually, the sugars added are glucose or sucrose. The acid produced through this fermentation (primarily lactic acid) contributes to the tanginess (acid taste) of the product, promotes water release as the pH is depressed to the iso-electric point of meat proteins to attain the desired final water activity (a.sub.w), provides safety against food-borne pathogens or production of enterotoxins, contributes to the final texture by the modification of meat proteins, and also plays a part in the fixing of the red color of meat. The acid producing starter cultures usually used belong to the genera Pediococcus and Lactobacillus. Only species that are relatively salt tolerant are used.
The secondary functions of starter bacteria used in dry and semi-dry sausages relate to the nitrate reducing activity which plays an important role in maintaining the red color, dissipating hydrogen peroxide generated by certain indigenous and contaminant lactic acid bacteria, and generating flavor compounds which impart the "mature sausage flavor". Hydrogen peroxide has deleterious effects on color and on fat by reacting with the red meat pigment and turning it to a green hue. As a powerful oxidant, it is also responsible for reacting with the fat to generate oxidized flavors. Therefore, the use of nitrate reducing and catalase producing genera in starter mixtures ensures good red color fixation and prevention of oxidized flavor defects. The bacterial species commonly used for these functions are Micrococcus varians (some authors include Micrococcus roseus) and Staphylococcus carnosus and Staphylococcus xylosus.
The flavor of sausages is derived from the salt, spices, acid generated by fermentation, various secondary metabolites of carbohydrate fermentation and by-products of proteolytic and lipolytic activity of starter and adventitious flora. Lactic acid bacteria used as starters have relatively mild proteolytic and lipolytic/esterolytic activities, while the micrococci and staphylococci possess more pronounced proteolytic and lipolytic enzymes. Peptides and amino acids derived through lactic acid bacterial metabolism could further be transformed into flavorful carbonyls, alcohols and esters by the micrococci and staphylococci. Proteolytic and lipolytic activities of the micrococci and/or staphylococci add on to these flavor imparting pool of components.
The flavor chemistry of fermented sausages and hams is quite complex. Berdague et al found more than 86 compounds that comprised the flavor components of dry sausages that were made without spices or other flavoring materials. These workers suggested that the origin of volatile flavor compounds in fermented sausages were the result of lipid oxidation (60%), fermentation (27%), proteolysis (6%) and other sources (7%). Stahnke and Zeuthen examined the volatiles from Italian Salami. They mentioned that some of the flavorful volatiles originate from spices, and others are degradation products of carbohydrates, protein and lipids brought about by microbial activity. They also stated that proteolytic breakdown products like free amino acids, peptides and nucleotides have a pronounced effect on the final taste of salamis, while lipolytic breakdown products like volatile fatty acids, aldehydes and ketones are of more importance to the aroma. The contribution of secondary metabolism of amino acids to the carbonyl and volatile fatty acid pool should also be considered to be significant in the flavor of fermented meats.
Among the more prominent flavor compounds in fermented sausages and hams mentioned by various investigators are two aldehydes: 3-methyl-butanal and 2-methyl butanal, (Hinrichsen L. and H. J. Anderson, Volatile Compounds and Chemical Changes in Cured Pork: Role of Three Halotolerant Bacteria, J. Agri. Food Chem. 42:1537-1542 (1994)); (Hinrichsen L. and S. B. Pedersen, Relationship among Flavor, Volatile Compounds, Chemical Changes, and Microflora in Italian-Type Dry-cured Ham During Processing, J. Agric. Food Chem 43:2932-2940 (1995)); (Hierro, E. et al, Effect of Selected Microorganisms on Dry Fermented Sausage Volatiles, Proceedings 41st Annual International Congress of Meat Science and Technology 1:251-252 (1995)); (Berdague et al, Effects of Starter Cultures on the Formation of Flavour Compounds in Dry Sausage, Meat Science 35:275-287 (1993)); (Kemner, M. K. et al, Aroma Formation with Starter Cultures in Meat Model Systems, Med. Fac. Landbouww. Univ. Gent 60/4a (1995)); (Stanhke, L. H., Dried Sausages Fermented with Staphylococcus xylosus at Different Temperatures and with Different Ingredient Levels--Part III. Sensory Evaluation, Meat Science 41:211-223 (1995)); and (Andersen, H., and L. Hinrichsen, Changes in Curing Agents, Microbial Counts and Volatile Compounds during Processing of Green Bacon using Two Different Production Technologies, J. Sci. Food. Agric. 68:477-487 (1995)). Hinrichsen and Andersen have discussed the various metabolic routes by which these methyl side-chain aldehydes could be derived. One of these pathways involves the deamination of the amino acid leucine followed by oxidative decarboxylation of the intermediate alpha-ketoisocaproate.
While Berdague et al describe the odor of 3-methyl-butanal as "rancid, sweaty, pungent", Hinrichsen and Pedersen report that this aldehyde may contribute to the "nutty, cheesy" notes of sausage flavor. Recently, Hagen et al, (Hagen, B. F., et al Addition of a bacterial Proteinase Reduces the Maturation Time of Dry Fermented Sausages., Abstract, 5th Symposium on lactic acid bacteria, Genetics, Metabolism and Application, Veldhoven, Holland, September 1996), reported on the use of a bacterial proteinase derived from Lactobacillus paracasei ssp. paracasei NCDO 151 to accelerate dry sausage ripening. They obtained higher sensory scores on maturity of flavor, color, hardness and other attributes. They noted that the concentration of 3-methyl-butanal and 2-methyl butanal were higher in the enzyme-containing sausages. It is preferred to use cultures rather than enzymes which must appear on the label.
The availability of free leucine in sausage systems inoculated with pediococci and micrococci was reported by Varnam and Sutherland (Varnam, A. H., and J. P. Sutherland, Fermented Sausages, Meat and meat products: technology, chemistry and microbiology Chapter 7:317-353 (1995)). This is important as background for the production of 3-methyl-butanal in fermented meat. In the dairy culture art, the production of 3-methyl-butanal by "malty" strains of Lactococcus lactis spp lactis was elucidated by MacLeod and Morgan (MacLeod P. and M. E. Morgan, Leucine Metabolism of Streptococcus lactis var. Maltigenes. I. Conversion of Alpha-Ketoisocaproic Acid to Leucine and 3-methyl-butanal, pages 1208-1214 (1955)). For a long time, such strains were named Streptococcus lactis var. maltigenes. Such strains could commonly be isolated from raw milk. These bacteria convert leucine to 3-methyl-butanal by deamination, followed by oxidative decarboxylation. In 1974, Miller et al, (Miller A., et al Lactobacillus maltaromicus, a New species Producing a Malty Aroma, Intern. J. Of System. Bacterio. 24:346-354 (1974)) described a raw milk lactobacilli that also produced a "malty" flavor in milk and broth systems. The "malty" flavor in this case was also attributed to 3-methyl-butanal. The organism was named Lactobacillus maltaromicus. A metabolic pathway similar to the lactococci may be operative in this Lactobacillus spp.
The use of lactococci or lactobacilli in general as acid producing starters in sausage systems is not favored because of their relative low salt tolerance. Lactococci or lactobacilli do not thrive at salt concentrations greater than 6.0%. In sausage systems, the brine salt concentration is around 6.0 to 6.5%. The application of malty lactococci or lactobacilli as an adjunct starter solely for flavor generation without acid production has not been so far considered in making fermented sausages.